1. Field of the Invention
The present general inventive concept relates to a developing apparatus and an image forming apparatus including the developing apparatus, and more particularly to a binary developing apparatus in electrophotography that includes a unit for mixing and supplying supply toner and a developer, and an image forming apparatus including the binary developing apparatus.
2. Description of the Related Art
The conventional binary developing apparatus that uses a developer formed of toner and carrier are illustrated in FIGS. 1A and 1B. The conventional binary developing apparatus includes a developing roller 15 for supplying toner so as to develop an electrostatic latent image formed on a photosensitive drum 10, a first mixing unit 14 for supplying the developer to the developing roller 15, a second mixing unit 16 for mixing the developer transferred from the first mixing unit 14 and supply toner supplied by a supply unit 22 through a supply path 20 of a toner supply unit (not shown), and transferring the mixture of the developer and the supply toner to the first mixing unit 14.
Around the photosensitive drum 10 are a charging roller 12 for charging an outer circumferential surface of the photosensitive drum 10, an exposure apparatus 13 for exposing the charged outer circumferential surface of the photosensitive drum 10, and a cleaning blade 17 for transferring a toner image on the photosensitive drum 10 onto a transfer belt 30 and removing the toner remaining in the photosensitive drum 10. A transfer roller 40 is disposed facing the photosensitive drum 10, with the transfer belt 30 passing therebetween.
The toner is consumed and the carrier is reused in a developing region where the photosensitive drum 10 and the developing roller 15 face each other. To supply the toner consumed in the developing region, the conventional binary developing apparatus previously measures a quantity of toner used for printing by using a bit counter or measures a density thereof by using a toner density sensor (not shown), and supplies a toner shortage from the toner supply unit 22.
As multifunctional printers or printers have been recently digitized, apparatuses for forming an image by using digital exposure apparatuses, such as laser scanners or LED heads, are most popular. Thus, a temporal quantity of consumed toner can be estimated by calculating a digital value corresponding to a quantity of printing. However, the actual quantity of consumed toner varies according to an environment where the toner or electrophotographic drum is being used. Further, the toner supply unit is a machine part and a supply quantity thereof varies, and thus it is necessary to check a quantity of toner supplied to the toner density sensor. The toner density sensor measures a density of the carrier near the toner density sensor by using a permeability sensor. The toner density sensor does not measure the density of toner but measures a quantity of remaining carrier.
Further, the toner supply unit includes a supply roller of which a shaft has a groove via which a toner may pass to quantitatively supply the toner. The supply toner supplied from the toner supply unit is injected into the developer of the developing apparatus when binary particles of the supply toners cohere since toners in a toner tank are frictionally charged to opposite polarities thereof or cohere on their own or due to pressure. The toner particles injected into the developer are charged onto and attached to the surface of the carrier of the developer. During this process, each toner is properly charged and attached to the surface of the carrier. Thus, the toner particles can be developed.
A quantity of the developer used has been recently reduced, owing to a small-size developing apparatus. In particular, it is now possible to maintain an image density by using a small quantity of the developer since a high quality pigment is added to the toner, owing to the high quality and low cost, and smaller particles of the carrier.
However, the conventional binary developing apparatus needs a time for mixing the developer since it is necessary to precisely measure a quantity of consumed toner, inject the toner into the carrier, and mix, charge, and distribute the toner injected into the carrier. A short time for mixing the developer results in insufficiently charging the toner, and transferring the toner that is not held onto the surface of the carrier to the developing region. To increase the time for mixing the developer, a spare stirring chamber (not shown) is further installed (for example, see patent document 1).
[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 9-325612
However, the developing device of patent document 1 has a problem of an increased size since the developing device includes the developing tank and a spare stirring chamber. Further, a developer is formed of a carrier of powders that apply a resin coating onto the surface of ferrite or magnetite and a toner having resin as a main component. Thus, when the toner and the carrier are mixed together while the developer is currently flowing, since a weight of the flowing developer differs from that of developer contained in the developing apparatus, as illustrated in FIG. 2, supply toner Tadd supplied from a toner supply unit is not blended in developer D, and thus the supply toner Tadd that is insufficiently charged and distributed is transferred to a developing region. Therefore, an image quality decreases, and an image is contaminated or the inside of the developer is contaminated. In particular, a high speed developer of A4 size has a shorter mixing time by about 25% than that of a developer of A3 size, and thus the conventional developer does not achieve a high-speed mixing time.